package PTA.javabianchengjichu2;

import java.util.Scanner;

public class ex21 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println(4 *(1.0 -1.0/3 +1.0/5 -1.0/7 +1.0/9 -1.0/11 +1.0/13));

    }
}
